Differential expression of Vibrio vulnificus capsular polysaccharide

Vibrio vulnificus is a human pathogen whose virulence has been associated w ith the expression of capsular polysaccharide (CPS). Multiple CPS types hav e been described; however, virulence does not appear to correlate with a pa rticular CPS composition. Reversible-phase variation for opaque and translu cent colony morphologies is characterized by changes in CPS expression, as suggested by electron microscopy of cells stained nonspecifically with ruth enium red. Isolates with opaque colony morphologies are virulent and appear to be more thickly encapsulated than naturally occurring translucent-phase variants, which have reduced, patchy, or absent CPS, Previously, we have s hown that the virulence of translucent-phase variants was intermediate betw een opaque-phase variants and acapsular transposon mutants, suggesting a co rrelation between virulence and the amount of CPS expressed, In the present study, CPS expression of phase variants and genetically defined mutants of V. vulnificus M06-24/O was examined by using a CPS-specific monoclonal ant ibody with an enzyme-linked immunosorbent assay, flow cytometry, and immuno electron microscopy. Semiquantitative analyses of CPS expression correlated well among these assays, confirming that the translucent-phase variant was intermediate in CPS expression and retained type I CPS-specific epitopes, Cell surface expression of CPS varied with the growth phase, increasing dur ing logarithmic growth and declining in stationary culture. Significantly g reater CPS expression (P = 0.026) was observed for cells grown at 30 degree s C than for those at 37 degrees C. These studies confirm that phase variat ion and virulence in V. vulnificus correlate with the amount of CPS express ed and demonstrate the fluidity of bacterial polysaccharide expression in r esponse to environmental conditions.